The invention relates to an internal combustion engine. In known internal combustion engines of a similar type, when they are operated with a fuel-air mixture which must be externally ignited, the disadvantage arises that this mixture ignites poorly, especially when it is kept lean in fuel. This causes a nonuniform torque output of the engine. Various attempts have been made to attain a sufficiently positive ignition and reaction of the fuel and air with each other while keeping the proportion of fuel as low as possible, with the intention being to attain a mixture enrichment near the ignition point in the ignition chamber by means of stratification. Beyond this, raising the temperature level in the ignition chamber permits an increase in the ignitability of the lean fuel-air mixture. However, the occurrence of spontaneous ignition and premature wear because of overly high temperatures must be avoided.
In a known apparatus, the temperature of the ignition chamber wall was controlled with this purpose in mind. This is accomplished by using a thermal pipe surrounding the ignition chamber which, so long as the ignition chamber is cold, prevents the immediate conduction of the heat produced there away to the cooled chambers of the internal combustion engine and assures that an increased heat conduction to the cooled walls of the internal combustion engine only appears at high temperatures which can be set as needed.
In this known apparatus, it was further proposed to permit the ignition spark gap to skip over between one electrode and the wall of the ignition chamber within the boundary layer. However, an increased leaning of the operational mixture and thus an increase in the wall temperature of the ignition chamber required for positive ignition, using spark plugs having hook-shaped electrodes, causes excessive overheating of the electrodes and glow sparking with subsequent thermal destruction of the plug. Also, a screw-inserted spark plug acts with the metal housing surrounding the ceramic part of the spark plug as a heat sink with respect to the ignition chamber, so that in the conventional spark plug, the temperature level in the area of the ignition electrodes is lowered in a disadvantageous manner. In the known device, the spark plug is disposed diametrically opposite the exit port of the transfer channel. In such an arrangement and with a high ratio of length to cross-sectional area of the ignition chamber, severe acoustical fluctuations have been found to occur upon the expansion following ignition.
In ignition chambers which must be supplied from the main combustion chamber with fresh fuel-air mixture, there is the problem of gas exchange, i.e., the problem of furnishing a fresh fuel-air mixture, preferably enriched and free of remnant gas, to the ignition location at the instant of ignition, in order to obtain positive ignition at all operational ranges. Various proposals have been made to this end, which are intended to cause a flushing effect of the ignition chamber after expansion has taken place upon the arrival of the fresh fuel-air mixture.
It has also been proposed to place the ignition spark gap directly at the entrance of the transfer channel into the combustion chamber (German Offenlegungsschrift No. 25 038 11), where it is assured that a fresh fuel-air mixture is present at the instant of ignition. However, this device has the disadvantage that because of the long electrode freely extending into the combustion chamber and because of the high conversion energy at the ignition location, this electrode is exposed to such high thermal stresses that it is immediately destroyed.